Doses Of Arginine Vasopressin Research Articles

Stimulation of aquaporin (AQP) gene expression in human fetal membrane explants

MEMBRANE EXPLANTS MARIE H. BEALL, SHENGBIAO WANG, FATANEH AMIDI, GENE LEE, MICHAEL G. ROSS, Harbor-UCLA Med. Ctr. (LA BioMed), Dept. of Ob/Gyn, Torrance, California OBJECTIVE: AQP water channels have been proposed as regulators of intramembranous water transfer and thus amniotic fluid (AF) volume. Alterations in fetal membrane AQPs have been reported in conditions of altered AF volume, but the factors regulating amnion AQP expression are unknown. Stressed fetuses with oligohydramnios exhibit increased levels of arginine vasopressin (AVP), a peptide known to stimulate kidney AQP expression. We sought to examine the regulation of AQP expression by AVP and oxytocin using an amnion explant culture model. STUDY DESIGN: Human amnion was collected under sterile conditions from term Cesarean deliveries. Amnion samples were placed in defined culture medium supplemented with fetal calf serum. Cultures were either untreated (controls), or were exposed to 1, 10 or 100 nM AVP or oxytocin added to the culture media. Each time and treatment dose was replicated in 4 samples. Cultures were harvested after 2, 10 or 20 hours, RNA was extracted and realtime PCR was performed. The relative expression of AQP1, 3 and 9, normalized to the expression of beta actin, was compared to time-matched controls. Data were analyzed by ANOVA. RESULTS: 100 nM AVP increased AQP1 and 3 expression significantly at 2 hours of treatment; the relative expression then returned to baseline. AQP9 expression increased after treatment for 20 hours with lower doses of AVP (1 nM and 10 nM). Oxytocin had no consistent effect on expression of any AQP. CONCLUSION: AVP increased the expression of AQPs in human amnion. Fetal membrane AQP expression may be regulated by the fetus via urinary excretion of endocrine factors, thus providing a mechanism for fetal regulation of intramembranous flow and AF volume.

Use of Vasopressin in a Canine Model of Severe Verapamil Poisoning: A Preliminary Descriptive Study

The purpose of this preliminary study was to evaluate the effect of arginine vasopressin (AVP) administration in a model of shock induced by calcium channel antagonist overdose and to determine endogenous serum AVP concentrations in calcium channel antagonist-induced shock. This was a controlled, randomized laboratory investigation based on a previously described canine model of verapamil toxicity. After induction of verapamil toxicity, animals in both the control and the experimental groups (n = 6 each) received a continuous infusion of verapamil. Experimental animals received an escalating dose of AVP, while control animals received an equal volume of 0.9% saline infusion. The hemodynamic end point was return of mean arterial pressure (MAP) to within 20% of baseline. Surviving animals were killed after 60 minutes. In the treatment group, administration of low-dose AVP (4 mU/kg/min) resulted in further declines in cardiac index and heart rate. No significant change was noted in MAP with low-dose AVP. A slight increase in MAP was noted with both escalating doses of AVP and equivalent volumes of normal saline. By the end of the 60-minute antidote/saline phase, the MAPs of the saline control group and the AVP experimental group were similar. The primary hemodynamic end point was not achieved in either the AVP or the saline control arm. Mean baseline serum AVP concentration in control animals was 5.8 pg/mL, increasing to 225 pg/mL during the toxicity phase. In an animal model of verapamil-induced shock, endogenous AVP levels increased nearly 40-fold compared with baseline levels. Escalating doses of exogenous AVP worsened cardiac index and failed to return MAP to within 20% of baseline.

Use of Vasopressin in a Canine Model of Severe Verapamil Poisoning: A Preliminary Descriptive Study

Objectives: The purpose of this preliminary study was to evaluate the effect of arginine vasopressin (AVP) administration in a model of shock induced by calcium channel antagonist overdose and to determine endogenous serum AVP concentrations in calcium channel antagonist–induced shock. Methods: This was a controlled, randomized laboratory investigation based on a previously described canine model of verapamil toxicity. After induction of verapamil toxicity, animals in both the control and the experimental groups (n= 6 each) received a continuous infusion of verapamil. Experimental animals received an escalating dose of AVP, while control animals received an equal volume of 0.9% saline infusion. The hemodynamic end point was return of mean arterial pressure (MAP) to within 20% of baseline. Surviving animals were killed after 60 minutes. Results: In the treatment group, administration of low-dose AVP (4 mU/kg/min) resulted in further declines in cardiac index and heart rate. No significant change was noted in MAP with low-dose AVP. A slight increase in MAP was noted with both escalating doses of AVP and equivalent volumes of normal saline. By the end of the 60-minute antidote/saline phase, the MAPs of the saline control group and the AVP experimental group were similar. The primary hemodynamic end point was not achieved in either the AVP or the saline control arm. Mean baseline serum AVP concentration in control animals was 5.8 pg/mL, increasing to 225 pg/mL during the toxicity phase. Conclusions: In an animal model of verapamil-induced shock, endogenous AVP levels increased nearly 40-fold compared with baseline levels. Escalating doses of exogenous AVP worsened cardiac index and failed to return MAP to within 20% of baseline.

Response of the hypothalamic-pituitary-adrenal axis to small dose arginine-vasopressin and daily urinary free cortisol before and after alprazolam pre-treatment differs in obesity

Arginine vasopressin (AVP) has a central role in the response of the hypothalamic-pituitary-adrenal (HPA) axis to stress conditions. A low dose of AVP has been shown to have a modest, but significant effect on ACTH response in normal weight subjects. The aim of this study was to test the response of the HPA axis in obese subjects in order to assess eventual primary neuroendocrine alterations, previously demonstrated by using AVP combined with corticotropin releasing hormone (CRH). In addition, given its central inhibitory action on the HPA axis, we investigated whether the suppressive capacity of alprazolam (APZ) pretreatment on the hormone response to low-dose AVP challenge and daily urinary free cortisol (UFC) excretion rate may be altered in the presence of obesity. Fifteen overweight or obese women and eight normal-weight controls randomly underwent two low-dose AVP tests (0.3 UI iv bolus), one without (AVP test) and the other preceded by APZ administration (0.5 mg at midnight and 0.5 mg 90 min before the test in the morning at 08:30 h) (APZ/AVP test). Blood samples for ACTH and cortisol assay were obtained at baseline and throughout each test. The day before each test, 24h-UFC/ creatinine was also mea-sured. Basal ACTH levels were similar in the two groups, whereas cortisol concentrations were significantly lower in the overweight/obese group. Overweight/obese women had higher ACTH and cortisol responses to the AVP tests and significantly greater hormone inhibition after APZ than controls. In both groups, AVP-induced delta-peak cortisol values before and after APZ pre-treatment were significantly correlated. Body fat distribution had no effect on the HPA axis response to AVP either before or after APZ. Moreover, APZ decreased 24h-UFC/creatinine values unsignificantly in controls and by approximately 50% in the overweight/obese subjects. These changes were unrelated to the cortisol response to the AVP test before and after APZ pretreatment. On the other hand, percent changes of 24h-UFC/creatinine after APZ were negatively related to the body mass index (BMI) but positively with waist circumference values, which indicates that the abdominal obesity phenotype may counteract the 24 h-UFC/creatinine that would be expected on the basis of BMI values. Our data further support the concept that in women obesity may represent a condition of hyperresponsiveness or hypersensitivity of the HPA axis to neuroendocrine stimuli, which appear to be independent of feedback control. In addition, the data on the inhibiting capacity of APZ on UFC excretion confirm that the alterations of the HPA axis in obesity is particularly evident in the abdominal phenotype.

Hemodynamics of Milrinone and Low-Dose Vasopressin Infusion during OPCAB

Background: AVP (arginine vasopressin) shows unique hemodynamic characterisics, as a vasopressor. AVP has been tried in many cathecholamine refractory vasodilatory situations, andsometimes resulted in effective hemodynamic improvement. In dis study, we hypothesized that low dose AVP infusion could recoverthe decreased SVR (systemic vascular resistance) induced by milrinone infusion with minimal effect on PVR (pulmonary vasculr resistance). Methods: Sixteen patients undergoing OPCAB participated in this study. After a loading dose milrinone was infused, low dose vasopressin infusion was started and titrated until the ssremic blood pressure increased by 20%. During the study, hemodynamic factors including pulmonary capillary wedge pressur and cardiac output were measured using a continuous thermodilution technique with a Swan-Ganz catheter. Results: Milrinone infusion reduced both SVR and PVR. And vasopressin infusion increased SVR, but show relatively less effect on PVR. Conclusions: Low-dose vasopressin infusion could be used to recover the SVR decrease caused by milirinone infusion with little effect on PVR.

Arginine-vasopressin in nucleus of the tractus solitarius induces hyperglycemia and brain glucose retention

Hypothalamic arginine-vasopressin (AVP) plays an important role both as a neurotransmitter and hormone in the regulation of blood glucose and feeding behavior. AVP-containing axons from the parvocellular subdivision of paraventricular nucleus of the hypothalamus terminate in the nucleus of the tractus solitarius (NTS), but the function of this projection is not known. Interestingly, the NTS also receives afferent information from the carotid body and other peripheral receptors involved in glucose homeostasis. We have previously reported that stimulation of the carotid body receptors initiates a hyperglycemic reflex and increases brain glucose retention. Here we show that direct administration of micro-doses of AVP into the NTS of anesthetized or awake rats rapidly increased the levels of blood glucose concentration and brain arterio–venous (A–V) glucose difference. This effect was not observed when the same doses of AVP were injected in the brainstem outside NTS. Arginine-vasopressin antagonist microinjections alone produced a small but significant reduction in brain A–V glucose. Pre-administered VP1-receptor antagonist [β-mercapto-β,β-cyclopentamethylene-propionyl 1, O-Me-Tyr 2,Arg 8]vasopressin blocked the effects of AVP. These results indicate that AVP acting on its receptors locally within the NTS participates in glucose homeostasis, increasing both blood glucose concentration and brain A–V glucose differences. Hypothalamic AVP may facilitate hyperglycemic responses initiated by peripheral signals processed at the level of the NTS.

Evidence that reduced renal medullary nitric oxide synthase activity of dahl s rats enables small elevations of arginine vasopressin to produce sustained hypertension.

On the basis of observations supporting the functional importance of nitric oxide (NO) in the regulation of renal medullary function, and a reduced nitric oxide synthase (NOS) enzyme activity in the outer medulla of the Dahl salt-sensitive (SS/Mcw) rats, we hypothesized that these inbred rats would have reduced capacity to synthesize renal medullary NO. This reduced capacity would sensitize them to the hypertensive effects of small elevations of circulating arginine vasopressin (AVP). SS/Mcw and Brown Norway (BN/Mcw) rats with implanted arterial and venous catheters were fed a 0.4% salt diet and infused intravenously for 14 days with a subpressor dose of AVP (2 ng/kg per min). Mean arterial pressure (MAP) was measured 2 hours daily in unanesthetized rats maintained in their home cages. MAP in SS/Mcw rats increased during day 1 of AVP infusion from a control level of 127+/-0.9 mm Hg to an average of 147+/-1.6 mm Hg after 14 days. MAP did not return to control values during the 3 days after the end of AVP infusion. BN/Mcw rats showed no changes of MAP during 14 days of AVP infusion (90.4+/-0.6 mm Hg and 92.3+/-0.4 mm Hg). Northern blot analysis of renal tissue from vehicle (saline) -infused rats demonstrated that NOS I and NOS III mRNA expression was significantly less in SS/Mcw rats in the renal outer medulla compared with BN/Mcw rats. We conclude that small, normally subpressor elevations of plasma AVP can produce chronic hypertension in SS/Mcw rats and that this phenomenon is related to the reduced medullary NOS enzyme activity, which in turn reduces the AVP-stimulated NO synthesis.

TNF-α Modulates Arteriolar Reactivity Secondary to a Change in Intimal Permeability

Inflammatory stimuli are often associated with marked changes in vascular reactivity. Tumor necrosis factor-alpha (TNF-alpha) is and important inflammatory cytokine with diverse effects including the ability to increase vascular endothelial cell permeability and to alter the structure of the endothelial cell glycocalyx. We have previously shown that arteriolar sensitivity to vasoactive materials is influenced by a barrier property of the arteriolar endothelium, and here we test the hypothesis that TNF-alpha might increase intimal permeability and thereby increase the access of circulating arginine-vasopressin (AVP) to vascular smooth muscle. Our objective in the current work was to show that TNF-alpha-mediated modulation of intimal cell permeability may produce both quantitative and qualitative alterations in vascular reactivity to arginine-vasopressin. Hamster cheek pouch arterioles (approximately 65 microm, i.d.) were double-cannulated and perfused. [Arg8]-vasopressin was applied selectively to either the luminal or the adventitial surface of isolated cannulated arterioles. The reactivity of the arterioles to vasopressin was determined in the presence and absence of TNF-alpha (0.625 microg/mL; 1 hour). Adventially applied AVP induced a concentration-dependent vasoconstriction with a threshold of approximately 1 pM, and a maximal constriction at 10 nM. In contrast, luminally applied AVP induced a biphasic response, showing a modest vasodilation in the range of 1 to 100 pM, and constrictions at doses higher than 1 nM. Maximal constrictions were not obtained with luminal doses of AVP as high as 1 microM; (i.e., at doses 100-fold higher than those that produced maximal responses with adventitial application). Dilations induced by luminal application of AVP were significantly attenuated by 10 microM Nomega-nitro-L-arginine methyl ester (L-NAME), but were not altered by 10 microM indomethacin. After treatment with TNF-alpha, the concentration-response curve for luminally applied AVP showed a more pronounced constriction and the dilator component of the agonist was eliminated. There was no change in the reactivity to adventitially applied AVP or to adventitial applications of acetylcholine. Nonspecific increases in endothelial cell permeability induced by 3-[(3-chloroamino-dopropyl)-dimethylamino]-1-propanesulfonate (CHAPS) also eliminated the potency differences between luminal and adventitial drug application. Following TNF-alpha treatment and loss of the dilator component of the response to AVP, L-NAME was still capable of reducing the arteriolar sensitivity to ACh, thus showing that the endothelial cell machinery for NO production was intact following TNF-alpha treatment. Our findings show that the reactivity of intact resistance vessels to agonists that have both endothelial-dependent and smooth muscle cell-dependent components will be complex. Reactivity is the summation of: 1) the relative sensitivities of smooth muscle and endothelial cells to AVP, 2) the release of nitric oxide or other mediators from endothelium, and 3) the restricted access of intraluminal AVP to arteriolar smooth muscle cells. Thus, cytokines, and perhaps other materials that regulate endothelial cell permeability, can modify arteriolar reactivity by altering transendothelial cell access of luminal stimuli to the smooth muscle cells, as well as by acting directly on smooth muscle or by influencing the production of endothelial cell-derived vasoactive materials. In the case of agonists that have an endothelial cell dilator component as well as a smooth muscle constrictor component, this may result in a qualitative change in response as is shown here with AVP.

Evidence That Reduced Renal Medullary NOS Activity of Dahl S Rats Enables Small Elevations of Avp to Produce Sustained Hypertension

27 It remains unclear why sustained elevations of plasma arginine vasopressin (AVP), a potent vasoconstrictor and fluid retaining hormone, do not generally result in hypertension. Related to this, there have been 4 general observations: 1) AVP is elevated in many forms of human and experimental hypertension, including Dahl S rats; 2) AVP can stimulate nitric oxide synthases (NOS) and nitric oxide (NO) production in the renal medulla of normal rats; 3) AVP stimulated NO production can buffer AVP induced reductions of medullary blood flow; 4) partial reduction of medullary NOS activity (via medullary L-NAME infusion) unmasks chronic hypertensive effects of small elevations of plasma AVP (Hypertension. 2000; 35:740-745). In the present study, we hypothesize that Dahl salt-sensitive rats (DS) have reduced capacity to synthesize medullary NO which sensitizes them to the hypertensive effects of small elevations of circulating AVP. DS and Brown Norway (BN) rats with implanted arterial and venous catheters were fed a 0.4% salt diet and infused continuously for 14 days with a chronic “subpressor” dose of AVP (2 ng/kg/min). Conscious mean arterial pressure (MAP) was measured 2 hours daily with rats maintained in their home cages. MAP in DS rats increased during day1 of AVP infusion from a control level of 127 ± 0.9 mmHg to an average of 147 ± 1.6 mmHg after 14 days. MAP did not return to control values even within three days following the end of AVP infusion. BN rats showed no changes of MAP during 14 days of AVP infusion (90.4 ± 0.6 mmHg and 92.3 ± 0.4 mmHg). Northern blot analysis of renal tissue from vehicle (saline) infused rats demonstrated that NOS I and NOS III mRNA expression was significantly less in DS rats in the renal outer medulla compared to BN rats. We conclude that small, normally subpressor elevations of plasma AVP can produce chronic hypertension in DS rats, a phenomenon probably related to reduced renal medullary NO synthesis.

Evidence That Reduced Renal Medullary NOS Activity of Dahl S Rats Enables Small Elevations of Avp to Produce Sustained Hypertension

27 It remains unclear why sustained elevations of plasma arginine vasopressin (AVP), a potent vasoconstrictor and fluid retaining hormone, do not generally result in hypertension. Related to this, there have been 4 general observations: 1) AVP is elevated in many forms of human and experimental hypertension, including Dahl S rats; 2) AVP can stimulate nitric oxide synthases (NOS) and nitric oxide (NO) production in the renal medulla of normal rats; 3) AVP stimulated NO production can buffer AVP induced reductions of medullary blood flow; 4) partial reduction of medullary NOS activity (via medullary L-NAME infusion) unmasks chronic hypertensive effects of small elevations of plasma AVP (Hypertension. 2000; 35:740-745). In the present study, we hypothesize that Dahl salt-sensitive rats (DS) have reduced capacity to synthesize medullary NO which sensitizes them to the hypertensive effects of small elevations of circulating AVP. DS and Brown Norway (BN) rats with implanted arterial and venous catheters were fed a 0.4% salt diet and infused continuously for 14 days with a chronic “subpressor” dose of AVP (2 ng/kg/min). Conscious mean arterial pressure (MAP) was measured 2 hours daily with rats maintained in their home cages. MAP in DS rats increased during day1 of AVP infusion from a control level of 127 ± 0.9 mmHg to an average of 147 ± 1.6 mmHg after 14 days. MAP did not return to control values even within three days following the end of AVP infusion. BN rats showed no changes of MAP during 14 days of AVP infusion (90.4 ± 0.6 mmHg and 92.3 ± 0.4 mmHg). Northern blot analysis of renal tissue from vehicle (saline) infused rats demonstrated that NOS I and NOS III mRNA expression was significantly less in DS rats in the renal outer medulla compared to BN rats. We conclude that small, normally subpressor elevations of plasma AVP can produce chronic hypertension in DS rats, a phenomenon probably related to reduced renal medullary NO synthesis.

Intravenous arginine-vasopressin in children with vasodilatory shock after cardiac surgery.

Recent investigations at our institution have studied a variety of vasodilatory shock states that are characterized by vasopressin deficiency and pressor hypersensitivity to the exogenous hormone. Our experience in adults prompted the use of arginine-vasopressin (AVP) in a similar group of critically ill children. This report describes our early experience (from February 1997 through April 1998) in 11 profoundly ill infants and children (5 male, 6 female) ages 3 days to 15 years (median, 35 days) treated with AVP for hypotension after cardiac surgery which was refractory to standard cardiopressors. Although underlying heart disease was present (congenital heart defects in 10 and dilated cardiomyopathy in 1), only 2 patients had severely depressed cardiac function as demonstrated by 2D echocardiogram before administration of AVP. All patients were intubated and receiving multiple catecholamine pressors and inotropes, including dobutamine (n=10), epinephrine (n=8), milrinone (n=7), and dopamine (n=4) before receiving AVP. Five patients received AVP intraoperatively immediately after cardiopulmonary bypass, 5 in the intensive care unit within 12 hours of surgery, and 1 on postoperative day 2 for hypotension associated with sepsis. The dose of AVP was adjusted for patient size and ranged from 0.0003 to 0.002 U. kg(-1). min(-1). During the first hour of treatment with AVP, systolic blood pressure rose from 65+/-14 to 87+/-17 mm Hg (P<0. 0001; n=11), and epinephrine administration was decreased in 5 of 8 patients and increased in 1. Plasma AVP levels before treatment were available in 3 patients and demonstrated AVP depletion (median, 4.4 pg/mL; n=3). All 9 children with vasodilatory shock survived their intensive care unit stay. The 2 patients who received AVP in the setting of poor cardiac function died, despite transient improvement in blood pressure. Infants and children with low blood pressure and adequate cardiac function after cardiac surgery respond to the pressor action of exogenous AVP. AVP deficiency may contribute to this hypotensive condition.

Intravenous Arginine-Vasopressin in Children With Vasodilatory Shock After Cardiac Surgery

Background —Recent investigations at our institution have studied a variety of vasodilatory shock states that are characterized by vasopressin deficiency and pressor hypersensitivity to the exogenous hormone. Our experience in adults prompted the use of arginine-vasopressin (AVP) in a similar group of critically ill children. Methods and Results —This report describes our early experience (from February 1997 through April 1998) in 11 profoundly ill infants and children (5 male, 6 female) ages 3 days to 15 years (median, 35 days) treated with AVP for hypotension after cardiac surgery which was refractory to standard cardiopressors. Although underlying heart disease was present (congenital heart defects in 10 and dilated cardiomyopathy in 1), only 2 patients had severely depressed cardiac function as demonstrated by 2D echocardiogram before administration of AVP. All patients were intubated and receiving multiple catecholamine pressors and inotropes, including dobutamine (n=10), epinephrine (n=8), milrinone (n=7), and dopamine (n=4) before receiving AVP. Five patients received AVP intraoperatively immediately after cardiopulmonary bypass, 5 in the intensive care unit within 12 hours of surgery, and 1 on postoperative day 2 for hypotension associated with sepsis. The dose of AVP was adjusted for patient size and ranged from 0.0003 to 0.002 U · kg −1 · min −1 . During the first hour of treatment with AVP, systolic blood pressure rose from 65±14 to 87±17 mm Hg ( P &lt;0.0001; n=11), and epinephrine administration was decreased in 5 of 8 patients and increased in 1. Plasma AVP levels before treatment were available in 3 patients and demonstrated AVP depletion (median, 4.4 pg/mL; n=3). All 9 children with vasodilatory shock survived their intensive care unit stay. The 2 patients who received AVP in the setting of poor cardiac function died, despite transient improvement in blood pressure. Conclusions —Infants and children with low blood pressure and adequate cardiac function after cardiac surgery respond to the pressor action of exogenous AVP. AVP deficiency may contribute to this hypotensive condition.

Altered pituitary sensitivity to corticotropin-releasing factor and arginine vasopressin participates in the stress hyporesponsiveness of lactation in the rat.

The regulation of the activity of the hypothalamic-pituitary-adrenal (HPA) axis is modified during lactation, wherein a blunted stress-induced adrenocorticotropic hormone (ACTH) and glucocorticoid secretion is coupled with elevated basal secretion of these hormones. The involvement of pituitary modifications in lactation-induced stress hyporesponsiveness has yet to be established. In this study we tested the hypothesis that the pituitary sensitivity to corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) is altered in lactation in the rat. We examined the effect of exogenous CRF (0.1-5 microg/rat), AVP (0.01-0.5 microg/rat), and AVP (0.01-0.5 microg/rat)+CRF (0.1 microg/rat) on the ACTH response of virgin, mid-lactating (lactation day 10-12) females, as well as nursing females separated from their pups for 48 h. Additionally, to determine if changes in CRF- or AVP-receptor densities might mediate alterations in pituitary sensitivity, we compared pituitary CRF- and AVP-receptor binding by autoradiography in pregnant, mid-lactating, and virgin female rats. While both virgin and lactating female rats exhibited significant ACTH responses to CRF, the responses to the highest doses of CRF (2.0 and 5.0 microg/rat) were greater in virgin than in lactating females. Separation of the litter for 48 h partially restored pituitary responsiveness to 2.0 microg of CRF. Conversely, whereas lactating females displayed robust ACTH secretion following a high dose of AVP or following a combination of AVP+CRF, the response of virgin females was much smaller. These modifications in pituitary responsiveness were not accompanied by significant differences in pituitary CRF-and AVP-receptors levels between female groups. Our results demonstrate that a reduction in pituitary sensitivity to CRF, but not to AVP occur during lactation in the rat which mediates, at least in part, the stress hyporesponsiveness of lactation.

Stress-induced suppression of pulsatile Luteinising hormone release in the female rat: role of vasopressin.

Insulin-induced hypoglycaemic (IIH) stress evokes the release of arginine vasopressin (AVP) and suppresses luteinising hormone (LH) pulses in a number of species, a phenomenon augmented by the presence of oestradiol (E2). The aim of this study was to test the hypothesis that AVP not only disrupts pulsatile LH secretion in the female rat, but specifically mediates the effect of IIH stress on suppressing LH release. The role of E2 in augmenting the disruptive effect of AVP on LH secretion was also addressed. Rats were ovariectomized (OVX) and fitted with intracerebroventricular (i.c.v. ) and intravenous (i.v.) cannulae. For experiments requiring comparisons of neuroendocrine responses in the presence and absence of E2, animals were implanted subcutaneously with E2 or oil-filled capsules respectively. AVP (5 microg) administered via the i.c.v. cannula suppressed LH secretion by decreasing LH pulse amplitude without affecting LH pulse frequency, an effect that was blocked by central administration of an AVP antagonist (25 microg). This inhibitory response was evident only in E2-replaced OVX rats, thus suggesting a sensitizing influence of the gonadal steroid. In the AVP-deficient Brattleboro rats, IIH stress did not interrupt pulsatile LH secretion as demonstrated in Long Evans and Wistar controls. While these data might suggest a pivotal role for AVP in stress-induced suppression of LH release, central administration of an AVP antagonist did not prevent the interruption of LH pulses in response to IIH stress. Furthermore, it would appear that AVP is not primarily involved in hypoglycaemic stress-induced suppression of pulsatile LH secretion since central administration of very high doses of AVP resulted in a suppression of LH pulse amplitude and not frequency, while hypoglycaemic stress caused an interruption of LH pulses.

The effects of analogs of the C-terminal fragment of arginine-vasopressin on the dynamics of development of a conditioned active avoidance response in rats.

This paper reports studies of the effects of original analogs of the C-terminal fragment AVP(6-9), D-MPR and D-MPRG, on the development of a conditioned active avoidance response in rats; agents were given intranasally over a wide range of doses. The most effective does of D-MPR was 0.1 microgram/kg, and the most effective dose of D-MPRG was 0.01 microgram/kg. The tri- and tetrapeptide doses were 10 and 100 times smaller than the dose of arginine-vasopressin used in analogous experimental conditions. The tri- and tetrapeptide accelerated development of the active avoidance conditioned response, affecting both formation of the habit and consolidation of the memory trace. The actions of these peptides were mainly on perception processes, i.e., isolation of the concrete stimulus from the environment, and assessment and remembering of its biological significance.

Effect of Ca2+ agonists in the perfused liver: determination via laser scanning confocal microscopy.

Ca2+ is a critical intracellular second messenger, but few studies have examined Ca2+ signaling in whole organs. The amplitude and frequency of Ca2+ oscillations encode important cellular information. Using laser scanning confocal microscopy in the indo 1 acetoxymethyl ester dye-loaded rat liver, we investigated the effect of various Ca2+ agonists that act at distinct mechanistic sites on Ca2+ signaling. Perfusion with suprathreshold doses of arginine vasopressin (AVP) (2-20 nM) caused a single Ca2+ wave that originated in the pericentral vein region and spread centrifugally to the periportal area. Lower doses of AVP (0.2-2 nM) caused multiple Ca2+ waves and Ca2+ oscillations. Perfusion with ATP (1. 4-17.5 microM) caused rapid transient elevations in intracellular free Ca2+ concentration ([Ca2+]i) occurring in isolated hepatocytes or groups of hepatocytes throughout the lobule and were of shorter duration than those due to AVP. Also in contrast to AVP, there was no specific anatomic location within the hepatic lobule that was more susceptible to ATP. Thapsigargin and cyclopiazonic acid did not cause a Ca2+ wave but rather produced a uniform and fairly simultaneous increase in [Ca2+]i in all hepatocytes in the lobule. Perfusion with 14 microM ryanodine produced a single transient spike in [Ca2+]i in a small number (<2%) of hepatocytes. Dantrolene, an inhibitor of Ca2+ release, reduced the increased [Ca2+]i occurring after AVP. Insight into the mechanism of action of these Ca2+-active compounds on Ca2+ signaling in the intact liver is provided.

Hormone-stimulated Ca2+ reabsorption in rabbit kidney cortical collecting system is cAMP-independent and involves a phorbol ester-insensitive PKC isotype

Hormones such as parathyroid hormone (PTH), arginine vasopressin (AVP), and prostaglandin E2 (PGE2) are generally believed to act through cAMP to stimulate active Ca2+ reabsorption in the distal part of the nephron. This study investigates the relationship between intracellular cAMP levels and the rate of Ca2+ reabsorption in immunodissected rabbit connecting and cortical collecting tubules cultured to confluence on permeable supports. Basolateral PTH, AVP, and PGE2 and apical adenosine dose dependently increased Ca2+ reabsorption from 48 to 110 nmol. hr-1. cm-2. Measurement of intracellular cAMP levels revealed that in the case of PTH and AVP, the dose-response curve for the increase in cAMP virtually matched that for transcellular Ca2+ transport. By contrast, with PGE2, this curve was shifted two decades to the right, whereas in the case of adenosine, no increase in cAMP was observed. The results with the latter two hormones disagree with the classic concept that Ca2+ reabsorption is stimulated via a cAMP-dependent mechanism. Furthermore, the potent adenylyl cyclase inhibitor 2', 5'-dideoxyadenosine (DDA; 100 micrometers) suppressed the PTH- and AVP-induced increase in cAMP completely without affecting Ca2+ reabsorption. Similarly, concentrations of PGE2, which maximally stimulated Ca2+ reabsorption without increasing cAMP, were not inhibited by DDA. The specific protein kinase C (PKC) inhibitor chelerythrine (5 micrometers) inhibited PTH-, AVP-, PGE2-, and adenosine-stimulated Ca2+ reabsorption by 77%, 67%, 79%, and 100%, respectively. Down-regulation of phorbol ester-sensitive PKC isotypes by prolonged (120 hr) treatment with 0.1 micrometers 12-O-tetradecanoylphorbol 13-acetate did not interfere with the inhibitory action of chelerythrine on hormone-stimulated Ca2+ transport. PTH, AVP, PGE2, and adenosine stimulate Ca2+ reabsorption via a pathway that is independent of cAMP and that involves a phorbol ester-insensitive PKC isotype.

Repeated stress, like vasopressin, sensitizes the excitatory effects of corticotropin releasing factor on the acoustic startle reflex

In the rat, evidence now suggests a neurotransmitter function for the neuropeptides arginine vasopressin (AVP) and corticotropin releasing factor (CRF), implicating them in various autonomic, behavioral, and neuroendocrine responses to stress. Repeated AVP/CRF release in the pituitary portal circulation, due to stress, sensitizes and potentiates the release of ACTH from the anterior pituitary. Using a neuroanatomically well-defined behavior, the acoustic startle reflex in the rat, we sought to determine whether an interaction between AVP, CRF and stress might also occur centrally as measured by increased behavioral sensitivity to AVP or CRF given directly into the brain. The first experiment tested whether repeated intraventricular (i.c.v.) infusion of AVP would lead to an increase in the excitatory effect of a subthreshold dose of AVP on the acoustic startle reflex when infused 48 h later. Different groups of rats were infused with various doses of AVP (0.3, 3, or 30 ng) or vehicle on Day 1 and tested for startle over the next 60 min. On Day 2, 48 h later, all animals were infused with a single dose of AVP (300 pg) and tested for startle. Infusion of AVP on Day 1 did not increase startle consistently at any dose, but did lead to a sensitized excitatory effect of AVP on startle on Day 2 which was non-monotonically related to the dose of AVP given on Day 1. Experiment 2 tested whether AVP on Day 1 would sensitize the excitatory effects on startle of CRF given i.c.v. on Day 2. Different groups of rats were infused i.c.v. with various doses of AVP (10, 30, 100, 300 pg) or vehicle on Day 1. On Day 2, 48 h later, all rats were infused with a subthreshold dose of CRF (0.25 μg). Infusion of AVP on Day 1 led to a sensitized excitatory effect of CRF on startle on Day 2 which was non-monotonically related to the dose of AVP given on Day 1. In experiment 3, we tested whether footshocks given on Day 1 would sensitize the excitatory effect of CRF on startle tested 48 h later. Different groups were given footshocks (0.2, 0.4, 0.8, 1.6 mA) on Day 1. On Day 2, 48 h later, all rats were infused with a subthreshold dose of CRF (0.25 μg). Footshocks given on Day 1 led to a sensitized excitatory effect of CRF on startle on Day 2 which was non-monotonically related to the intensity of footshock on Day 1. Taken together, these results suggest that an interaction between AVP, CRF and stress may occur centrally, consistent with other studies showing similar interactions peripherally. This may provide a model system for analyzing how prior stress leads to enhanced behavioral reactions to subsequent stressors and a mechanism to explain dysregulation of the stress response.

Phosphorylation of the V2 Vasopressin Receptor

The V2 vasopressin receptor undergoes ligand-induced sequestration and desensitization (Birnbaumer, M., Antaramian, A., Themmen, A. P. N., and Gilbert, S. (1992) J. Biol. Chem. 267, 11783-11788). The V2 receptor expressed in transfected cells labeled with [32P] orthophosphate was phosphorylated following the addition of 100 nM arginine vasopressin (AVP). Phosphorylation was complete 5 min after addition of AVP, and was not stimulated by increased levels of Ca2+ or cAMP. The half-maximal dose of AVP that stimulated phosphorylation was 2.4 +/- 0.4 nM, similar to the receptor KD of 4. 5 +/- 0.4 nM. The role of phosphorylation on receptor desensitization was investigated by studying two vasopressin receptors 14 and 27 amino acids shorter than the wild type receptor. The missing segments were not needed for normal ligand binding or coupling to Gs, but the last 14 amino acids were required for phosphorylation. The truncated receptors exposed to 100 nM AVP were sequestered and desensitized. The R137H V2R mutant receptor that binds vasopressin with wild type-like affinity and does not couple to Gs (Rosenthal, W., Antaramian, A., Gilbert, S., and Birnbaumer, M. (1993) J. Biol. Chem. 268, 13030-13033) was phosphorylated and subjected to ligand-induced sequestration. These results established that phosphorylation is not essential for sequestration and desensitization of the V2 vasopressin receptor. Furthermore, they revealed that the conformation acquired after ligand occupancy is necessary for receptor phosphorylation and sequestration, while coupling to Gs is not.

Cytochrome P-450-dependent HETEs: profile of biological activity and stimulation by vasoactive peptides.

The cytochrome P-450 pathway is capable of metabolizing arachidonic acid to omega- and subterminal hydroxylase metabolites, 16-, 17-, 18-, 19-, and 20-hydroxyeicosatetraenoic acids (P-450 HETEs). We have quantitated, by gas chromatography-mass spectrometry (GC/MS), endogenous HETEs exiting the rabbit isolated perfused kidney elicited by hormonal stimulation. Kidneys were perfused with Krebs-Henseleit solution containing indomethacin (2.8 microM) to prevent further metabolism of HETEs by cyclooxygenase. Phenylephrine (2-3 microM) was added to the perfusate to raise perfusion pressure to approximately 80 mmHg. Angiotensin II (ANG II), arginine vasopressin (AVP), and bradykinin (BK) were injected into the renal artery and perfusates collected throughout the vasoactive response. After addition of an internal standard, deuterated 19-HETE, perfusates were extracted and purified and P-450 HETEs were derivatized for GC/MS analysis. Under basal conditions, 16-, 18-, 19-, and 20-HETEs were released (range: 50-270 pg/ml), 19-HETE being the highest and fivefold greater than 16-HETE, the lowest. Injection of 50 ng ANG II increased by two- to sixfold P-450 HETE release associated with an increase of 40 +/- 11 mmHg in perfusion pressure. An equipressor dose of AVP (50 ng) did not release P-450 HETEs nor did a 5-micrograms dose of the vasodilator peptide BK, which decreased perfusion pressure by 22 +/- 6 mmHg. Authentic 19- and 20-HETE isomers resulted in dose-dependent dilation, as did 18(R)- and 16(R)-HETEs, whereas their enantiomers and 17-HETE isomers were without effect on perfusion pressure. The vasodilator effects of 18(R)- and 16(R)-HETEs, like 20- and 19-HETEs, were inhibited by indomethacin. Furthermore, P-450 HETEs exhibited both regio- and stereoselective inhibition of proximal tubule adenosine triphosphatase (ATPase) activity. The (S) enantiomers of 16- and 17-HETE potently inhibited activity, whereas their (R) isomers and other P-450 HETEs had negligible effects on ATPase activity. The quantity of HETEs released from the kidney, either under basal conditions or when stimulated by ANG II, and their biological profile suggest that subterminal HETEs may participate in renal mechanisms affecting vasomotion and tubular transport.